The present disclosure relates to electric machines and more specifically to a rotated reverse-direction-staple system and method for securing lamination plates of an electric machine to one another.
Electric machines, such as motors, generators, alternators, starter-generators, typically have a stator core and/or a rotor core formed of a plurality of stacked lamination plates. The stacked lamination plates are commonly held together along the axial dimension by welding, cleating, or conventional interlocking.
The welding and cleating methods add cost and time to the manufacturing process since these methods are performed after the lamination plates are pressed and stacked.
During conventional interlocking, each lamination plate is stamped so that an indentation is formed on one side of the plate and a protrusion extends from the opposite side of the plate. Typically, the protrusion extends in a downward direction from the lamination plates. The lamination plates are then stacked so that the downward protrusion of a first lamination plate is received in and forms an interference fit with the indentation of a subsequent lamination plate. Thus, conventional interlocked lamination plates can be formed during the pressing and stacking operation and, thus can be less costly than other methods.
However, the conventional interlocked lamination plates can form a core that is “spongy” or breaks apart during subsequent manufacturing operations, which has limited the height of the stack. Additionally, the conventional interlocked lamination plates require extreme accuracy and tolerances in the punching operation, which can add cost and complexity to the manufacturing process. For example, the position of the interlocking protrusion and indentation between the subsequent lamination plates must be very accurate in order to ensure the required interference fit. In addition, the tolerances between the punch and the die require extreme close punch to die clearance (e.g., conventional interlock requires about 0.0002 inches clearance) in order to ensure the required interference fit. Moreover, the position and number of the interlocking protrusion/indentations can cause eddy currents in the electric machine, which reduces the efficiency of the electric machine.
The stacked lamination plates are typically stamped from a piece of stock material. The stock material can have a variation in thickness along its length and/or width, commonly known as gamma. When stacking lamination plates, the gamma can cause the stack to be distorted. Specifically, the resultant stack can be curved with respect to its longitudinal axis when each lamination plate is stacked on top of one another so that its thickness variation is located in the same location (i.e., non-rotated laminations). Thus, it has become common to rotate each lamination with respect to one another so that the gamma is evenly distributed about the longitudinal axis, which results in a straight stack.
Accordingly, there is a continuing need for methods of stamping lamination plates of an electric machine and securing those plates to one another in a straight stack and products formed thereby that eliminate one or more of the aforementioned drawbacks and deficiencies of the conventional methods. Moreover, there is a continuing need for methods of stamping and securing lamination plates to form a tightly secured and straight stack as the lamination plates are being assembled in the stamping process.